1. Field of the Invention
This invention relates to a process for producing vanadium chlorides by chlorinating vanadium oxides. More particularly, this invention relates to a process for producing vanadium oxytrichloride (VOCl.sub.3) and vanadium tetrachloride (VCl.sub.4) by reacting chlorine and carbon with vanadium pentoxide (V.sub.2 O.sub.5) wherein the effluent stream from the process is substantially free of vanadium chlorides and chlorine.
2. Description of the Prior Art
Vanadium chlorides, such as vanadium oxytrichloride (VOCl.sub.3), vanadium tetrachloride (VCl.sub.4) and mixtures thereof, are used as components of co-catalyst systems for olefin polymerization.
Various methods are known for preparing vanadium oxytrichloride. According to Inorganic Syntheses, Volume 4, New York, 1953 page 80, vanadium pentoxide is reduced with hydrogen or carbon at a temperature in the range of from 600.degree. C. to 1000.degree. C. to vanadium trioxide, which is then transformed into vanadium oxytrichloride by a treatment with chlorine at a temperature of 500.degree.-600.degree. C. The final product obtained is strongly contaminated with vanadium tetrachloride and chlorine and, therefore repeated distillation over sodium is recommended for purification.
U.S. Pat. No. 3,355,244 to Carter et al., describes a process for preparing vanadium oxytrichloride by maintaining vanadium oxide, a carbon and an inert diluent in a fluidized bed and fluidizing the bed with chlorine. The gaseous reaction products recovered overhead from the fluidized bed are initially passed into a cyclone separator to remove any entrained solids. The resulting crude vanadium oxytrichloride gases are then fed to a quench condenser wherein they are quenched in a counter current circulating stream of liquid vanadium oxytrichloride. The condensed vanadium oxytrichloride product is then subsequently treated, e.g. by fractional distillation, to obtain a highly purified vanadium oxytrichloride product. The gaseous effluent stream, from this process, however, contains unrecovered vanadium chlorides and unreacted chlorines, necessitating the use of expensive auxiliary equipment to remove these products and reducing yields by wasting chlorine, vanadium and vanadium chlorides.
The production of vanadium tetrachloride and vanadium oxytrichloride mixtures by the intereaction of vanadium pentoxide, carbon and chlorine at elevated temperatures is known from Z. Chem. 2, 376-7, (1962). The basic reaction is known from U.S. Pat. No. 1,415,028 to
Methods are known for producing vanadium tetrachloride. British Pat. No. 1,308,738 describes the chlorination of vanadium pentoxide in a fluidized bed of particulate vanadium pentoxide and carbon at 425.degree. C. The resultant product stream containing predominantly vanadium oxytrichloride is then chlorinated in a second fluidized bed at 600.degree. C. in the presence of activated carbon to produce a product stream containing predominantly vanadium tetrachloride and minor quantities of vanadium oxytrichloride. The vanadium oxytrichloride and vanadium tetrachloride are then separated by fractional distillation.
Thus, generally, vanadium chlorides, such as vanadium oxytrichloride and vanadium tetrachloride are prepared by subjecting a vanadium oxide or vanadium oxide ore to the action of chlorine at elevated temperatures in the presence of a reactant carbon to produce a gas stream containing gaseous vanadium chlorides. Usually this gas stream contains, in addition to vanadium chlorides, carbon dioxide, carbon monoxide and unreacted chlorine. The bulk of the vanadium chlorides are separated from the gas mixture by condensation. However, as a result of the comparatively high vapor pressures of the vanadium chlorides, substantial amounts thereof will remain in the effluent stream along with the carbon dioxide and unreacted chlorine.
The vanadium chlorides remaining in the effluent stream after condensation, will generally amount to from about 2 to about 10% of the total vanadium chlorides produced, but most likely about 2 to about 4%. Obviously, such amounts of vanadium chlorides in the effluent stream along with the loss of unreacted chlorine represents a large economic loss as well as a pollution problem.
All of the prior art processes suffer from the fact that the effluent stream from the process must be treated to remove the pollutants therefrom, e.g. chlorine, vanadium tetrachloride etc. Such treatment is typically accomplished with complicated and expensive apparatus and with no increase in yields or process efficiency.
For example, the effluent stream from the reaction of vanadium oxide with chlorine and carbon typically can contain carbon dioxide, carbon monoxide, chlorine vanadium oxytrichloride and minor quantities of vanadium tetrachloride. Known prior art methods of purifying such a gaseous effluent stream would consist of a caustic scrubbing process or absorption by CCl.sub.4. Caustic scrubbing is costly in energy requirements and capital equipment and only converts an air pollution problem into a water pollution problem. Absorption of chlorine and vanadium oxytrichloride using CCl.sub.4, besides being costly in energy requirement and capital equipment, affords only a partial solution to the problem, for excessive amounts of CCl.sub.4 will be added to the gas effluent stream. Neither of these methods of purifying the effluent stream would increase product yields.